Method for operating an ultracentrifuge and a suitable centrifuge for said method



Sept. 24, 1968 KARL.-HEINZ ROMER 3,402,883

METHOD FOR OPERATING AN ULTRACENTRIFUGE AND A SUITABLE CENTRIFUGE FOR SAID METHOD Filed Nov. 23, 1965 2 Sheets-Sheet 1 Fig.1

g Fig.2

Sept. 24, 1968 KARL-HEINZ RGMER 3,402,883

METHOD FOR OPERATING AN ULTRACENTRIFUGE AND A SUITABLE CENTRIFUGE FOR SAID METHOD Filed Nov. 23, 1965 2 Sheets-Sheet 2 Fig. 3'

United States Patent ABSTRACT OF THE DISCLOSURE Method for the operation of an ultracentrifuge and centrifuge for practicing the method, where the vessels in the centrifuge are vertically disposed and in operation are swung into horizontal position by centrifugal forces.-

In the method the motor for the centrifuge is first operated at a low speed so that the vessels are only moved outwardly to a somewhat inclined position, and then the centrifuge motor is operated at full power to swing the vessels into horizontal position. In operation a liquid is placed in the vessels, the density of which increases upwardly, and the substance to be contrifuged is placed into the vessel with this liquid.

The invention relates generally to centrifuges and to methods for operating such devices in order to achieve certain results in methods of analysis.

More in particular, the invention relates to a method for operating an ultracentrifuge having centrifuging vessels that are swung into horizontal position during operation.

A centrifuging vessel for use in a centrifuge of this type is described, for example, in German patent specification 1,171,178 and in US. Patent No. 3,202,348 which also discuss the problems arising particularly with'density gradient centrifuging. In density gradient centrifuging a liquid is first filled into the centrifuging vessel in which the density decreases upwardly from the bottom. The substance to be analyzed is then introduced in the form of a layer of liquid on top of the liquid having the density gradient. The extremely high accelerations which arise with a rapidly rotating centrifuge and with the centrifuging vessels pointing essentially horizontally outwardly, cause a sedimentation, the duration and other physical characteristics of which permit conclusions to be drawn about the substance which is being analyzed. As explained in the patent specifications mentioned above, an entire series of problems arise especially with very rapidly running centrifuges, as a result of which it is not possible to obtain very sharp separation of the individual substances of different densities. Thus, it has been found, for example, that the result is very much affected in a harmful manner if the moment of torsion arising during starting and braking is imparted to the liquid or substance in the centrifuging vessels. It has been accomplished by means of expedient measures, which are not of especial interest here, to prevent the circulating of the liquid resulting from such a moment of torsion. A further problem with centrifuges of this type could only be solved in that the centrifuging vessels were provided with a sector-shaped sedimentation space. In spite of the use of these expedients, it was found that at some time during the centrifuging operation there exists the possibility for the particular substances to mix relatively strongly at their adjacent surfaces. This effect must be eliminated as much as possible in order to obtain clear boundaries for the individual super-imposed layers.

The invention is based on the surprising discovery that 3,402,883 Patented Sept. 24, 1968 the undesired mixing takes place at the very beginning of the starting action. Since with a low number of revolutions, for example, immediately after the start of the centrifuge, the normal acceleration effective in the axial direction of the column of liquid is still small, the acceleration caused by the increase in the velocity that is effective perpendicularly to the axial direction of the column of liquid can cause displacements in the column of liquid. This phenomenon retreats into the background only then, when a speed of several hundred revolutions per minute is attained and the normal acceleration which increases as the square of the number of revolutions has attained a value which is large as compared to the angular acceleration.

Based on this concept, it is proposed in accordance with the invention that the initiation of the start takes place at greatly reduced motor power. It is therefore required in accordance with the invention to carry through the initiation of the start at as slow an acceleration as possible, so that the tangential acceleration which is effective perpendicularly to the direction of the axis of the liquid column cannot cause the undesired displacement of the individual layers of liquid.

For carrying out the method in accordance with the invention, a centrifuge with an electric motor is suitable where the control means comprise this electric motor in series with a nheostat that is connected in parallel with a short-circuit switch. This short-circuit switch can be actuated by means of a timing device in such a manner that it is close-d after an adjustable period of time counting from the initiation of the start.

In addition to the control of the motor of a centrifuge which is known at any rate where the current supplied is maintained essentially constant, it is accomplished by means of such a resistance that the angular acceleration is small, especially at the initiation of the start, i.e., until the centrifuging vessels are essentially horizontal due to the effect of the centrifugal force. When this position of the centrifuging vessels is attained, the tangential acceleration which then becomes relatively small has no further possibility to cause the effect described above.

The inventive concept can also be materialized in that the electric motor used for driving is connected in series with a potentiometer, the resistance of which decreases from the initiation of the start beginning at the maximum value. In this connection it has proven to be very effective to construct the potentiometer as a motor potentiometer' which is controlled by the revolution indicator that refietcs the number of revolutions of the rotor. Such revolution indicators have been known long since and are built in with most of the heavy-duty centrifuges. It is also possible, however, to provide a transmission for adjusting the potentiometer which, as the case may be, is driven by a centrifugal or friction coupling by the drive motor. This latter form of construction has proven itself in practice especially well due to its compact shape, small inclination to failure, and simple manner of operation.

Further advantages and details of the invention will become apparent from the following description of two embodiments with reference to the drawing, in which FIG. 1 is a schematic illustration of a centrifuge for carrying out the method in accordance with the invention;

FIG. 2 is a partial view showing a second possibility for mechanically controlling the resistance which is conneoted in series with the motor; and

FIG. 3 illustrates a third embodiment of the invention schematically. t

In FIG. 1 a housing 1 is indicated which is closed by means of a cover 2 which has an aperture through which projects the shaft 4 that is driven by the motor M. The housing 1 may be evacuated. The shaft 4 carries at its upper end a disk 8, at the edge of which a vessel 6 is supported at a pivot 5. The vessel 6 is thus pivotable in that plane which is defined by a radius of the disk 8 and the shaft 4. The centrifuging vessel is indicated in solid lines at 6 in the position of rest and in interrupted lines at 6 in that position which it assumes during rapid rotation under the effect of the centrifugal force. An intermediate position of the vessel is indicated at 6. The liquid having a gradient of density is identified by a and the substance to be analyzed by b. It can be seen in the position indicated at 6" how the substance b moves in a known manner downwardly under the efie'ct of the centrifugal forces, i.e., to the right as shown in the drawing. To this extent the centrifuge has been known long since.

In the manner illustrated the motor M is connected to the power line which may, for example, provide a single phase current or direct current. The resistor R is connected in series with one lead and is shunted by a switch S. A timing device Z controls the opening and closing of the switch as indicated by the arrow. In carrying out the method in accordance with the invention it is necessary at first during the initiation of the start to hold the switch S in the open position, i.e., to set the timing device accordingly, and to close the same after a predetermined time period determined particularly by the characteristics of the centrifuge and the material to be centrifuged, so that the total potential supplied no longer drops across the motor and the resistor R but is applied to the motor alone. In this circuit setting the centrifuge then attains its desired maximum number of rotations.

A second possibility for carrying out the method in accordance with the invention is schematically illustrated in FIG. 2, where for the sake of clearness the housing and its contents have been omitted. Only the shaft 4 and the aperture 3 are indicated. In this embodiment it is possible, for example, as indicated at 7, to bring the motor shaft out through the bottom and drive a transmission G by way of a coupling K. The coupling K may suitably be a centrifugal force coupling which opens upon attaining a predetermined number of revolutions, thus separating the transmission G from the motor M, or an electromagnetic coupling which separates after a predetermined time period, or simply a loosely operating friction coupling. As indicated at 9, the transmission operates the movable arm A of a potentiometer P as determined by the rotation of the motor. The potentiometer here is connected in series with the motor M. The operation of the arm A is, of course, possible by a push bar or a worm gear, or any similar means for transmitting power known to the man skilled in the art.

As already mentioned above, it is also possible, of 1 course, to short-circuit the resistor which is in series with the motor under the control of the rotation indicator of known construction by suitable movement of the pickup arm A on the potentiometer P.

The resistor connected in series with the motor must I necessarily be so great when the method in accordance with the invention is carried out, and when the device or arrangement also proposed in accordance with the invention is used, that the motor M on being connected develops only a very small moment of rotation, and accordingly runs at first very slowly, and thus also permits the rotor to start slowly until at about 200 to 400 r.p.m. the normal acceleration has attained a value which is large as compared to the corresponding angular acceleration. Then the resistor R, or P, can from an electrical point of view be eliminated from the series circuit with the motor M, and the motor M operates at full potential.

FIG. 3 shows another embodiment of the invention in a diagram where the housing 1 and its contents are omitted. Only the shaft 4 of the motor and the passage 3 for the shaft between the motor M and the rotor, which is not illustrated, are indicated. Also here the motor shaft 4 may be extended through the motor M and be connected to a revolution indicating device which is schematically indicated at D. This device controls the motor potentiometer by way of conductors 10. The motor potentiometer comprises an electric motor M which moves the slider or arm A over the resistor R to vary the potential drop. In this embodiment one lead of the power line is connected directly to the motor M while the other wire or lead is connected to the motor M, as illustrated, by way of the slider A and that part of the resistor R which is between the slider A and motor M. The revolution meter or indicator controls the motor M of the motor potentiometer by way of leads 10 in such a manner that with a low number of revolutions of the centrifuge motor M the resistance R has a substantial portion of its total length connected in series with the motor, while with increasing numbers of revolution of the motor M the revolution meter D controls the motor M in such a manner that the slider A is moved from the left to the right as seen in the drawing so that for high numbers of revolution the resistor R is no longer in series with the motor.

All details illustrated are of importance for the invention.

Having now described my invention with reference to the embodiments illustrated in the drawings, I do not wish to be limited there-to, but what I desire to protect by Letters Patent of the United States is set forth in the appending claims.

I claim:

1. Method for the operation of an ultracentrifuge of the type having centrifuging vessels that are swung into horizontal position during operation by means of centrifugal forces;

said method comprising the steps of placing a liquid the density of which decreases upwardly into the centrifuging vessel,

introducing the substance to be centrifuged into the vessel,

initiating the operation of the centrifuge motor at low power until a relatively low centrifuge speed is attained, and

then increasing the power of the centrifuge motor to full power.

2. The method in accordance with claim 1 where said low centrifuge speed is between 200 and 400 r.p.m.

3. Centrifuge for practicing the method of centrifuging where a liquid of upwardly decreasing density is placed into the centrifuging vessel, the centrifuge motor is initiated at low power until a speed of between 200 and 400 r.p.m. is attained and then the motor is operated at a higher power;

said centrifuge comprising a vessel supporting means,

at least one centrifuging vessel pivotally supported on said supporting means for pivotal movement from suspended position into substantially horizontal position,

motor means for driving said supporting means including a shaft, and

control means including a resistance element connected in series with said motor means for controlling the speed of said motor means to operate at a predetermined low speed and switch means operative to change the resistance of said resistance element to operate at a predetermined higher speed.

4. Centrifuge in accordance with claim 3, where said switch means include a short-circuit switch connected in parallel with said resistance element and an adjustable timing device associated with said short-circuit switch operative to close said h-ort-circuit switch after a predetermined time period from the initiation of the start of the motor.

5. Centrifuge in accordance with claim 3, where said resistance element is a potentiometer connected in series with said motor means and having an operating arm, and said motor means includes a rotation indicator connected to said arm and operative to change the resistance of said potentiometer from a maximum to zero.

5 6 6. Centrifuge in accordance with claim 3, where said the resistance of said potentiometer from a maximum to potentiometer is a motor potentiometer operatively conzero. nected with said motor means, and said motor means includes a rotation indicator adapted to control said po- References Cited tentiometer in accordance with the number of rotations of 5 UNITED STATES PATENTS the o r- 3,202,348 8/1965 Strohmaier 233-26 7. Centrifuge in accordance with claim 3, where said 3,243,105 3/1966 A d 233-1 resistance element is a potentiometer having an operating arm and a transmission gear is operatively associated with HENRY T. KLINKSIEK, Primary Examiner. said motor means and connected to said arm for changing 10 

